Broadly, the invention relates to the combination of a valve and a means for operating the valve. More specifically, the invention is directed to a valve which is operated by a key member, the key member being a safety device.
In the chemical, the petrochemical, and the refinery industries many chemical reactions, or separations, are conducted in an apparatus referred to as a reactor vessel, or a distillation vessel. For those reactions which involve high pressures, the reactor is usually equipped with safety devices to prevent the possibility of explosions. In one type of safety system a conduit from the vessel connects the vessel into a pressure switch, and a shut off valve is usually installed in the conduit between the vessel and the switch. The switch is usually connected electrically to an alarm system, which has direct control over the reactor. The pressure switch is set at a predetermined limit which is considered a safe operating pressure. If the pressure in the reactor exceeds the limit setting, it will close the circuit to the pressure switch, which, in turn, will activate the alarm system and immediately shut down the reactor.
A routine safety procedure calls for periodically checking the operation of the alarm system. The procedure should include checking out the operation of the pressure switch, but frequently this is not done. To check the operation of the pressure switch, the switch must first be isolated from the reactor by closing the valve ahead of the switch. Closing the valve, therefore, adds an additional hazard if the technician should forget to open the valve after the safety check has been completed. The hazard can be further compounded if there is no periodic check of the pressure switch, since a malfunction in the switch could result in failure to activate the alarm system during a condition of overpressure in the reactor.